The present invention relates to industrial robots and more particularly to improvements in the articulation of a first arm on a base member, a second arm on the remote end of the first arm, and the transmission means for imparting movement to said second arm relative to said first arm.
A conventional horizontal articulation type industrial robot is shown in FIGS. 1-3, inclusive, and is comprised of a first horizontally disposed arm 3 rotatably mounted on a stationary vertical shaft 2 which in turn is secured to a stand 1. A first arm drive motor 4 is secured to the end of the first arm 3 which is pivotally mounted on the shaft 2 by suitable bearing means. A second horizontally disposed arm 5 is pivotally mounted on the free end of the first arm 3 for rotation about a vertically disposed shaft. A conventional tool, such as a gripping hand 7, is coupled to the free end of the second arm 5. A drive motor 6 for rotating the second arm 5 is mounted on the free end of the first arm 3. Planet type reduction gears are located within the housings 8 and 9 for operatively coupling the drive motors 4 and 6 to the first arm 3 and the second arm 5, respectively.
The details of the conventional planet type reduction gearing between the first and second arms is shown in FIG. 2 which is a sectional view of the portion in FIG. 1 designated by the reference numeral A. The planet type reduction gearing 10 located within the housing 9 is comprised of an input element 10a which is fixed for rotation with the drive shaft of the drive motor 6 by means of a key 11. An output element 10b which is in the form of a cup whose outer wall is provided with a number of small teeth, is connected to an output shaft 12 for rotation therewith. The teeth on the cup-shaped output element 10b are adapted to mesh with the teeth 10c which are secured to the housing 9. The output shaft 12 is rigidly connected to the second arm 5 by means of bolts 13 and pins 14 so that upon rotation of the output shaft 12 the second arm 5 will rotate relative to the first arm 3 about a vertical axis defined by the axis of the output shaft 12 and the drive shaft of the motor 6. The output shaft 12 is rotatably mounted in bearings 15 formed in the end of the first arm 3. The output shaft 12 is restrained against axial movement by means of a nut 16 threaded on the end thereof and a bearing washer 17 interposed between the nut 16 and the bearing 15.
In the operation of the conventional horizontal articulation type robot as disclosed in FIGS. 1 and 2, the first arm 3 and the second arm 5 are of substantially similar construction and therefore the operation of the second arm only will be described. The second arm drive motor 6 is rotated in accordance with instructions received from a separate non-illustrated control device. The rotation of the motor 6 is transmitted through the reduction gear 10 so that the rotation is reduced in accordance with a reduction gear ratio. The output shaft 12 secured to the output element of the reduction gear 10 is therefore rotated at a lower speed. This rotation causes the second arm 5 to swing about the axis defined by the output shaft 12 with a minimal amount of play due to the arrangement of the bearings 15, bearing nut 16 and bearing washer 17. The first arm 3 is swung about the vertically disposed axis of the stationary shaft 2 upon operation of the drive motor 4, the output shaft of which is coupled to the first arm 3 by means of a single gear reduction.
In the conventional horizontal articulation type robot disclosed in FIGS. 1-3, the second arm drive motor 6 is provided on the free end of the first arm so that when the first arm is driven, the inertial load on the first arm drive motor 4 is quite large. Furthermore, the second arm 5 is supported by the ball bearing 15 at the free end of the first arm as shown in FIG. 2, and accordingly the longitudinal length of the first arm is quite large, thereby substantially increasing the weight of the first arm 3 along with the inertial moment. Therefore, in order to operate the conventional robot at high speeds, it is essential that the first arm drive motor 4 is provided with a relatively large drive capacity. Thus, the conventional robot is disadvantageous in that it becomes unnecessarily bulky and heavy.
Furthermore, in the conventional robot, as shown in FIGS. 1-3, the end portion of the first arm 3 is recessed in the form of a gate for supporting the second arm 5. Therefore, if the operating range of the second arm 5 is relatively large, as shown in FIG. 3, than the recessed portion has to be increased accordingly, thereby decreasing the rigidity of the arm. Thus, the conventional robot suffers from the disadvantage that it is necessary to increase the thickness of the portions of the arm defining the gate in order to increase the rigity of the arm. The problem can be solved by making the operating range of the arm smaller, but this is also disadvantageous for obvious reasons. Finally, the conventional robot suffers from a further disadvantage inasmuch as the first and second motors are located on the first arm 3, thereby creating a complicated power supply and control arrangement for the motors due to the difficulty in leading wires to the respective motors.
Japanese Patent Publication No. 55-112789 discloses a robot similar to that disclosed in FIGS. 1-3 of the present application inasmuch as the motor for driving the first horizontally disposed arm about a vertical pivot shaft on a support member is mounted on the support member whereas the second motor for driving a second horizontally disposed arm about the second vertical pivot shaft carried by the free end of the first arm is mounted on the free end of the first arm in alignment with the second pivot shaft. Thus, the weight of the first arm is substantially increased and due to the gate type supporting arrangement for both the first and second arms, the range of pivotal movement of the first and second arms is substantially restricted.
Japanese Patent Publication No. 56-62778 discloses a different form of robot wherein the first arm is pivoted for movement about a support intermediate the ends of the first arm. A second arm is pivotally mounted on one end of the first arm and the drive motor of the second arm is mounted at the opposite end of the first arm. A drive shaft extends through the first arm to drive suitable gearing located in the gate type connection between the first and second arms. Thus, the first arm carries the extra weight of the motor and the gate type connection between the first and second arms limits the freedom of the second arm.